Home About us Contact
|
Home About us Contact | ||
|
|
||
Manganese
Terms modified by Manganese Selected AbstractsSelective Oxidation of Acetophenones Bearing Various Functional Groups to Benzoic Acid Derivatives with Molecular OxygenADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Ryota Nakamura Abstract Acetophenones substituted by alkyl, alkoxy, acetoxy, and halogen groups were selectively oxidized with molecular oxygen to the corresponding benzoic acids by using the N,N,,N,, -trihydroxyisocyanuric acid (THICA)/cobalt(II) acetate [Co(OAc)2] and THICA/Co(OAc)2/manganese(II) acetate [Mn(OAc)2]. For example, 4-methylacetophenone was selectively oxidized with molecular oxygen to 4-acetylbenzoic acid (85%) by THICA/Co(OAc)2 and to 4-methylbenzoic acid (93%) by Mn(OAc)2, while terephthalic acid was obtained in 93% with the THICA/Co(OAc)2/Mn(OAc)2 catalytic system. It is interesting that the acetyl group on the aromatic ring is efficiently converted by a very small amount of Mn(OAc)2 to the corresponding carboxylic acid, and that the present method provides a versatile route to acetylbenzoic acids which are difficult to prepare by conventional methods. [source] Manganese cell labeling of murine hepatocytes using manganese(III)-transferrin,CONTRAST MEDIA & MOLECULAR IMAGING, Issue 3 2008Christopher H. Sotak Abstract Manganese(III)-transferrin [Mn(III),Tf] was investigated as a way to accomplish manganese-labeling of murine hepatocytes for MRI contrast. It is postulated that Mn(III),Tf can exploit the same transferrin-receptor-dependent and -independent metabolic pathways used by hepatocytes to transport the iron analog Fe(III),Tf. More specifically, it was investigated whether manganese delivered by transferrin could give MRI contrast in hepatocytes. Comparison of the T1 and T2 relaxation times of Mn(III),Tf and Fe(III),Tf over the same concentration range showed that the r1 relaxivities of the two metalloproteins are the same in vitro, with little contribution from paramagnetic enhancement. The degree of manganese cell labeling following incubation for 2,7,h in 31.5,µm Mn(III),Tf was comparable to that of hepatocytes incubated in 500,µm Mn2+ for 1,h. The intrinsic manganese tissue relaxivity between Mn(III),Tf-labeled and Mn2+ -labeled cells was found to be the same, consistent with Mn(III) being released from transferrin and reduced to Mn2+. For both treatment regimens, manganese uptake by hepatocytes appeared to saturate in the first 1,2,h of the incubation period and may explain why the efficiency of hepatocyte cell labeling by the two methods appeared to be comparable in spite of the ,16-fold difference in effective manganese concentration. Hepatocytes continuously released manganese, as detected by MRI, and this was the same for both Mn2+ - and Mn(III),Tf-labeled cells. Manganese release may be the result of normal hepatocyte function, much in the same way that hepatocytes excrete manganese into the bile in vivo. This approach exploits a biological process,namely receptor binding, endocytosis and endosomal acidification,to initiate the release of an MRI contrast agent, potentially conferring more specificity to the labeling process. The ubiquitous expression of transferrin receptors by eukaryotic cells should make Mn(III),Tf particularly useful for manganese labeling of a wide variety of cells both in culture and in vivo. Published in 2008 by John Wiley & Sons, Ltd. [source] Heavy Metals in Matrices of Food Interest: Sequential Voltammetric Determination at Trace and Ultratrace Level of Copper, Lead, Cadmium, Zinc, Arsenic, Selenium, Manganese and Iron in MealsELECTROANALYSIS, Issue 18 2004Clinio Locatelli Abstract The voltammetric methods are very suitable and versatile techniques for the simultaneous metal determination in complex matrices. The present work, regarding the sequential determination of Cu(II), Pb(II), Cd(II), Zn(II) by square-wave anodic stripping voltammetry (SWASV), As(III), Se(IV) by square-wave cathodic stripping voltammetry (SWCSV) and Mn(II), Fe(III) by square-wave voltammetry (SWV) in matrices involved in foods and food chain as wholemeal, wheat and maize meal, are an interesting example of the possibility to sequentially determine each single element in real samples. Besides the set up of the analytical method, particular attention is aimed either at the problem of possible signal interference or to show that, using the peak area Ap as instrumental datum, it is possible to achieve lower limits of detection. The analytical procedure was verified by the analysis of the standard reference materials: Wholemeal BCR-CRM 189, Wheat Flour NIST-SRM 1567a and Rice Flour NIST-SRM 1568a. Precision, as repeatability, and accuracy, expressed as relative standard deviation and relative error, respectively, were lower than 6% in all cases. In the presence of reciprocal interference, the standard addition method considerably improved the resolution of the voltammetric technique. Once set up on the standard reference materials, the analytical procedure was transferred and applied to commercial meals sampled on market for sale. A critical comparison with spectroscopic measurements is also discussed. [source] Body distribution of trace elements in black-tailed gulls from Rishiri Island, Japan: Age-dependent accumulation and transfer to feathers and eggsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2005Tetsuro Agusa Abstract Body distribution and maternal transfer of 18 trace elements (V, Cr, Mn, Co, Cu, Zn, Se, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, Hg, Tl, and Pb) to eggs were examined in black-tailed gulls (Larus crassirostris), which were culled in Rishiri Island, Hokkaido Prefecture, Japan. Manganese, Cu, Rb, Mo, and Cd showed the highest levels in liver and kidney, Ag, Sb, and Hg in feather, and V, Sr, and Pb in bone. Maternal transfer rates of trace elements ranged from 0.8% (Cd) to as much as 65% (Tl) of maternal body burden. Large amounts of Sr, Ba, and Tl were transferred to the eggs, though maternal transfer rates of V, Cd, Hg, and Pb were substantially low. It also was observed that Rb, Sr, Cd, Cs, and Ba hardly were excreted into feathers. Concentrations of Co in liver, Ba in liver and kidney, and Mo in liver increased significantly with age, whereas Se in bone and kidney, Hg in kidney, and Cr in feather decreased with age in the known-aged black-tailed gulls (2,20 years old). It also was suggested that feathers might be useful to estimate contamination status of trace elements in birds, especially for Hg on a population basis, although the utility is limited on an individual basis for the black-tailed gulls. To our knowledge, this is the first report on the maternal transfer rate of multielements and also on the usefulness of feathers to estimate contamination status of Hg in birds on a population basis. [source] Synthesis, Structures, and Magnetic Properties of N -Trialkylsilyl-8-amidoquinoline Complexes of Chromium, Manganese, Iron, and Cobalt as well as of Wheel-Like Hexanuclear Iron(II) and Manganese(II) Bis(8-amidoquinoline)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2010Astrid Malassa Abstract The transamination of 8-(tert -butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8-(tert -butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8-(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8-(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8-aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8-amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8-amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8-amidoquinoline)manganese(II) (8) and bis(8-amidoquinoline)iron(II) (9), form hexamers with wheel-like molecular structures consisting of metal-centered nitrogen octahedra interconnected by common N···N edges. The cobalt complex, bis(8-amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6 -wheel 9 yield very close-lying ferromagnetically and antiferromagnetically coupled states. [source] Dinuclear Manganese and Cobalt Complexes with Cyclic Polyoxovanadate Ligands: Synthesis and Characterization of [Mn2V10O30]6, and [Co2(H2O)2V10O30]6,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 34 2009Shinnosuke Inami Abstract An all-inorganic complex, [Mn2{(VO3)5}2]6, (1), was synthesized, and the structure determination reveals a dinuclear manganese complex coordinated by two cyclic pentavanadate ligands. The cyclic pentavanadate units sandwich the edge-sharing octahedral dimanganese core through coordination of the oxido group of the pentavanadate. A dinuclear cobalt complex with a cyclic decavanadate, [Co2(OH2)2(VO3)10]6, (2), was also synthesized. The structure analysis reveals a dinuclear cobalt complex with a macrocyclic decavanadate, which is composed of 10 VO4 units joined by the vertex sharings. The CoO6 octahedrons are edge-shared, with each cobalt octahedron coordinated to five oxido groups from the decavanadate. The remaining site is occupied by water. The coordinated water molecules are supported with hydrogen bonds in two directions. Complex 2 in acetonitrile shows no reactivity with dioxygen even at low temperature, and the cyclic voltammogram of 2 shows no redox chemistry in acetonitrile. Complex 2 exhibits chromism by water exposure both in the solid state and in acetonitrile. Complex 2 is green,yellow in color, and the addition of water causes the complex to turn brown. After heating the sample, it returns to its original color in a reversible manner. The EXAFS data in acetonitrile is also reported and is consistent with the solid-state structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Using Chiral Ligand Substituents To Promote the Formation of Dinuclear, Double-Stranded Iron, Manganese, and Zinc MesocatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2007Stuart D. Reid Abstract The synthesis and structures of dinuclear manganese, iron, and zinc complexes of chiral di-iminodipyrromethane ligands (L) are reported. Schiff base condensation reactions between 5,5,-diformyl-2,2,-dipyrromethane and the chiral amines (,)-(R)-CH(Me)tBu and (+)-(R)-CH(Me)Ph result in the straightforward synthesis of the new, chiral ligands H2L2 and H2L3, respectively. Salt elimination reactions between K2L and divalent Mn and Fe halides, and protonolysis reactions between ZnMe2 and H2L result in the formation of the new dinuclear complexes [M2(L)2]. Investigation of the structures of these compounds in solution and in the solid state reveal that chiral mesocates are formed for L = L2, whereas for L = L3, a racemic mixture of helicates is present.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, Structure and Magnetic Behaviour of Manganese(II) Selenolate Complexes ,1[Mn(SePh)2], [Mn(SePh)2(bipy)2] and [Mn(SePh)2(phen)2] (bipy = bipyridyl, phen = phenanthroline)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2007Andreas Eichhöfer Abstract The manganese selenolate complex ,1[Mn(SePh)2] has been prepared by reaction of Mn(OOCCH3)2 with 2 equiv.PhSeSiMe3 in thf. In the crystal structure, the compound forms one-dimensional chains, and the bridging selenolate ligands result in relatively short metal,metal contacts of about 3 Å. Reaction with two equivalents of the Lewis bases 2,2,-bipyridine and 1,10-phenanthroline yielded the monomeric octahedral complexes [Mn(SePh)2(2,2,-bipy)2] and [Mn(SePh)2(1,10-phen)2], respectively. The magnetic and optical properties of these complexes have been investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, Crystal Structure, and Magnetic Properties of Two Manganese(II) Polymers Bearing Ferrocenecarboxylato LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2007Zilu Chen Abstract Reactions of Mn(ClO4)2·6H2O with FcCO2Na [Fc = (,5 -C5H4)Fe(,5 -C5H5)] in methanol solution gave [Mn3(FcCO2)6(CH3OH)4]n (1), and, in the presence of 4,4,-bipyridine (4,4,-bpy), [Mn3(FcCO2)6(H2O)2(4,4,-bpy)]n (2). Both complexes have the similar chains with a sequence of ,Mn,(,2 -COO)n,Mn,(,2 -COO),Mn,(,2 -COO),Mn,(,2 -COO)n,Mn, (n = 4 and 2 for complex 1 and 2, respectively), which are constructed alternatively from mononuclear [MnII] units and dinuclear [Mn2(FcCO2)4] units by ,2 -ferrocenecarboxylato- O,O, bridging. The two MnII ions in the dinuclear [Mn2(FcCO2)4] units of complex 1 are connected by four ferrocenecarboxylato ligands to form a swastika-like shaped skeleton, which is rare in metallocenecarboxylato complexes. However, the two MnII ions in the dinuclear [Mn2(FcCO2)4] units of complex 2 are bridged only by two carboxylato ligands, and the other two ferrocenecarboxylato ligands in this unit bind in a chelating mode. The chains in complex 2 are further interconnected by the coordinated 4,4,-bipyridine molecules to form two-dimensional coordination sheets. Magnetic susceptibility measurements revealed a weak antiferromagnetic coupling for both complexes. A model Heisenberg chain comprising classical spins coupled through alternating exchange interactions J1,J1,J2 (AF1,AF1,AF2) is proposed to describe the magnetic behavior. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Preparation of Hydroxylamine and O -Methylhydroxylamine Complexes of Manganese and RheniumEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Gabriele Albertin Abstract Hydroxylamine and O -methylhydroxylamine complexes [M(NH2OH)(CO)nP5,n]BPh4 and [M(NH2OCH3)(CO)nP5,n]BPh4 [M = Mn, Re; n = 1, 2, 3; P = P(OEt)3, PPh(OEt)2, PPh2OEt] were prepared by allowing hydrides MH(CO)nP5,n to react first with triflic acid and then with an excess of hydroxylamine. Bidentate phosphane and phosphite can also be used to prepare both NH2OH and NH2OCH3 complexes of manganese and rhenium of the [M(NH2OR)(CO)2(P,P)-{P(OEt)3}]BPh4 and [M(NH2OR)(CO)3(P,P)]BPh4 [R = H, CH3; P,P = Ph2POCH2CH2OPPh2, Ph2PO(CH2)3OPPh2, Ph2PN(CH3)CH2CH2N(CH3)PPh2] types with the use of MH(CO)2(P,P){P(OEt)3} and MH(CO)3(P,P) as precursors. The complexes were characterized spectroscopically and by theX-ray crystal-structure determination of [Re(NH2OCH3)(CO)2{PPh(OEt)2}3]BPh4 and [Re(NH2OCH3)(CO)3{Ph2PO(CH2)3OPPh2}]BPh4. Oxidation of the hydroxylamine complexes with Pb(OAc)4 was studied at ,40 °C and led to an unstable compound tentatively characterized as a nitroxyl [M],N(H)=O derivative.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Phase Relations Between ,-Tricalcium Phosphate and Hydroxyapatite with Manganese(II): Structural and Spectroscopic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2006Isaac Mayer Abstract The preparation of Mn-containing ,-tricalcium phosphate (,-TCP) samples was achieved in two ways: a) transformation of precipitated Mn-containing calcium hydroxyapatite (HA) to ,-TCP by heating at 1100 °C, and b) preparation by solid-state reaction of a mixture of CaCO3, (NH4)2HPO4, and Mn(NO3)2 at 1100 °C. Powder X-ray diffraction (XRD) analyses of the samples, obtained by both methods, show well-defined patterns with structural data of the rhombohedral R3c, ,-TCP phase. The calculated lattice constants are smaller than those known for ,-Ca3(PO4)2 because of substitution of Ca2+ by Mn2+. EPR spectroscopy indeed reveals that manganese is divalent in the samples. Apparently, the Ca(5) site in the ,-TCP structure is occupied by Mn2+. The distribution of Mn2+ between the ,-TCP and the HA phase in the case of preparation (b) was studied by EPR spectroscopy, and a pronounced preference for the former lattice was found. Micron- and submicron-sized crystals with visible faces were observed by TEM in the case of ,-TCP prepared by solid-state reaction, and large micron-sized, droplike-shaped crystals, sensitive to beam radiation, were found in the case of samples prepared by heating HA at elevated temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] A 2D Thiocyanato-Bridged Copper(II)-Manganese(II) Bimetallic Coordination Polymer with Ferromagnetic InteractionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2005Jing-Min Shi Abstract The first ferromagnetic coupled, thiocyanato-bridged copper(II)-manganese(II) bimetallic 2D polymer {[Cu(ipa)2]2Mn(NCS)6·2H2O}n (ipa = 1,2-propanediamine) has been synthesised and characterised by a single-crystal X-ray structure determination and variable temperature magnetic susceptibility studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Great Framework Variation of Polymers in the Manganese(II) Maleate/,,,,-Diimine System: Syntheses, Structures, and Magneto-Structural CorrelationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2003Chengbing Ma Abstract Three novel manganese(II) coordination polymers, [Mn (maleate)(phen)]n (1; phen = 1,10-phenanthroline), [Mn(maleate)(phen)]n·nH2O (2), and [Mn(maleate)(bpy)]n (3; bpy = 2,2,-bipyridine), have been synthesized by treatment of Mn2+ with maleic acid with participation of chelate diimine ligands, and have been identified by single-crystal X-ray diffraction to have either one-dimensional (1D) zigzag chain structures (1 and 2) or a two-dimensional (2D) sinuous layer structure (3). Each maleate dianion coordinates to three Mn centers, in different bridging modes (syn - anti in 1 and 2, syn - syn and anti - anti in 3). These compounds represent an interesting example of structural topology variation from 1D to 2D mediated by chemically similar auxiliary chelate ligands. Variable-temperature magnetic susceptibility measurements show weak anti-ferromagnetic exchange interactions between the adjacent MnII ions, with J = ,0.06 cm,1 (2) and J = ,1.3 cm,1, zJ, = ,0.27 cm,1 (3). The differences in the magnitudes of these coupling interactions agree well with the nature of the carboxylate-bridging coordination of maleate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Microfibril-associated glycoprotein-1 binding to tropoelastinFEBS JOURNAL, Issue 14 2004Multiple binding sites, the role of divalent cations Microfibrils and elastin are major constituents of elastic fibers, the assembly of which is dictated by multimolecular interactions. Microfibril-associated glycoprotein-1 (MAGP-1) is a microfibrillar component that interacts with the soluble elastin precursor, tropoelastin. We describe here the adaptation of a solid-phase binding assay that defines the effect of divalent cations on the interactions between MAGP-1 and tropoelastin. Using this assay, a strong calcium-dependent interaction was demonstrated, with a dissociation constant of 2.8 ± 0.3 nm, which fits a single-site binding model. Manganese and magnesium bestowed a weaker association, and copper did not facilitate the protein interactions. Three constructs spanning tropoelastin were used to quantify their relative contributions to calcium-dependent MAGP-1 binding. Binding to a construct spanning a region from the N-terminus to domain 18 followed a single-site binding model with a dissociation constant of 12.0 ± 2.2 nm, which contrasted with the complex binding behavior observed for fragments spanning domains 17,27 and domain 27 to the C-terminus. To further elucidate binding sites around the kallikrein cleavage site of domains 25/26, MAGP-1 was presented with constructs containing C-terminal deletions within the region. Construct M1659, which spans a region from the N-terminus of tropoelastin to domain 26, inclusive, bound MAGP-1 with a dissociation constant of 9.7 ± 2.0 nm, which decreased to 4.9 ± 1.0 nm following the removal of domain 26 (M155n), thus displaying only half the total capacity to bind MAGP-1. These results demonstrate that MAGP-1 is capable of cumulative binding to distinct regions on tropoelastin, with different apparent dissociation constants and different amounts of bound protein. [source] Manganese in biogenic magnetite crystals from magnetotactic bacteriaFEMS MICROBIOLOGY LETTERS, Issue 2 2009Carolina N. Keim Abstract Magnetotactic bacteria produce either magnetite (Fe3O4) or greigite (Fe3S4) crystals in cytoplasmic organelles called magnetosomes. Whereas greigite magnetosomes can contain up to 10 atom% copper, magnetite produced by magnetotactic bacteria was considered chemically pure for a long time and this characteristic was used to distinguish between biogenic and abiogenic crystals. Recently, it was shown that magnetosomes containing cobalt could be produced by three strains of Magnetospirillum. Here we show that magnetite crystals produced by uncultured magnetotactic bacteria can incorporate manganese up to 2.8 atom% of the total metal content (Fe+Mn) when manganese chloride is added to microcosms. Thus, chemical purity can no longer be taken as a strict prerequisite to consider magnetite crystals to be of biogenic origin. [source] Theoretical studies on high-valent manganese porphyrins: Toward a deeper understanding of the energetics, electron distributions, and structural features of the reactive intermediates of enzymatic and synthetic manganese-catalyzed oxidative processesISRAEL JOURNAL OF CHEMISTRY, Issue 1 2000Abhik Ghosh We present here a relatively comprehensive theoretical study, based on nonlocal density functional theory calculations, of the energetics, electron distributions, and structural features of the low-lying electronic states of various high-valent intermediates of manganese porphyrins. Two classes of molecules have been examined: (a) compounds with the general formula [(P)MnX2]0 (P = porphyrin; X = F, Cl, PF6) and (b) high-valent manganese-oxo species. For [(P)Mn(PF6)2]0, the calculations reveal a number of nearly equienergetic quartet and sextet states as the lowest states, consistent with experimental results on a comparable species, [(TMP)Mn(ClO4)2]0 (TMP = tetramesitylporphyrin). In contrast, [(P)MnCl2]0 and [(P)MnF2]0 have a single well-defined S = 3/2 Mn(IV) ground state, again in agreement with experiment, with the three unpaired spins largely concentrated (>90%) on the manganese atom. Manganese(IV)-oxo porphyrins have an S = 3/2 ground state, with the three unpaired spins distributed approximately 2.3:0.7 between the manganese and oxygen atoms. The metal-to-oxygen spin delocalization, as measured by the oxygen spin population, for MnIV = O porphyrins is less than, but still qualitatively similar to, that in analogous iron(IV)-oxo intermediates, indicating that the MnIV = O bond is significantly weaker than the FeIV = O bond in an analogous molecule. Thus, the optimized metal,oxygen bond distances are 1.654 and 1.674 Å for (P)FeIV(O)(Py) and (P)MnIV(O)(Py), respectively (Py = pyridine). This is consistent with the experimental observation that MnIV = O stretching frequencies are over 10% lower than FeIV = O stretching frequencies for analogous compounds. For [(P)Mn(O)(PF6)]0, [(P)Mn(O)(Py)]+, and [(P)Mn(O)(F)]0, the ground states clearly correspond to a (dxy)2 Mn(V) configuration and the short Mn,O distances of 1.541, 1.546, and 1.561 Å for the three compounds, respectively, reflect the formal triple bond character of the Mn,O interaction. Interestingly, the corresponding Mn(IV)-oxo porphyrin cation radical states are calculated to be a few tenths of an electrovolt higher than the Mn(V) ground states, suggesting that the Mn(IV)-oxo porphyrin cation radicals are not likely to exist as ground-state species. [source] Asymmetric Epoxidation of Olefins by Manganese(III) Complexes Stabilised on Nanocrystalline Magnesium OxideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2006M. Choudary Abstract The asymmetric epoxidation of unfunctionalised olefins to epoxides is realised by using manganese(III) complexes stabilised on nanocrystalline magnesium oxide in the presence (1R,2R)-(,)-diaminocyclohexane as a chiral ligand in good yields and up to 91,% enantiomeric excess. [source] Manganese potentiates nuclear factor-,B-dependent expression of nitric oxide synthase 2 in astrocytes by activating soluble guanylate cyclase and extracellular responsive kinase signaling pathwaysJOURNAL OF NEUROSCIENCE RESEARCH, Issue 9 2008Julie A. Moreno Abstract Inflammatory activation of glial cells is associated with neuronal injury in several degenerative movement disorders of the basal ganglia, including manganese neurotoxicity. Manganese (Mn) potentiates the effects of inflammatory cytokines on nuclear factor-,B (NF-,B)-dependent expression of nitric oxide synthase 2 (NOS2) in astrocytes, but the signaling mechanisms underlying this effect have remained elusive. It was postulated in the present studies that direct stimulation of cGMP synthesis and activation of mitogen-activated protein (MAP) kinase signaling pathways underlies the capacity of Mn to augment NF-,B-dependent gene expression in astrocytes. Exposure of primary cortical astrocytes to a low concentration of Mn (10 ,M) potentiated expression of NOS2 mRNA and protein along with production of NO in response to interferon-, (IFN,) and tumor necrosis factor-, (TNF,), which was prevented by overexpression of dominant negative I,B,. Mn also potentiated IFN,- and TNF,-induced phosphorylation of extracellular response kinase (ERK), p38, and JNK, as well as cytokine-induced activation of a fluorescent NF-,B reporter construct in transgenic astrocytes. Activation of ERK preceded that of NF-,B and was required for maximal activation of NO synthesis. Independently of IFN,/TNF,, Mn-stimulated synthesis of cGMP in astrocytes and inhibition of soluble guanylate cyclase (sGC) abolished the potentiating effect of Mn on MAP kinase phosphorylation, NF-,B activation, and production of NO. These data indicate that near-physiological concentrations of Mn potentiate cytokine-induced expression of NOS2 and production of NO in astrocytes via activation of sGC, which promotes ERK-dependent enhancement of NF-,B signaling. © 2008 Wiley-Liss, Inc. [source] Temporal responses in the disruption of iron regulation by manganeseJOURNAL OF NEUROSCIENCE RESEARCH, Issue 8 2006Catherine Kwik-Uribe Abstract Manganese (Mn) is an essential trace element, though at elevated exposures it is also a neurotoxicant. Several mechanisms underlying manganese toxicity have been investigated, although a consistent mechanism(s) of action at low exposures has not been fully elucidated. Here we systematically evaluated the effects of in vitro manganese exposure on intracellular iron (Fe) homeostasis and iron-regulatory protein (IRP) binding activity in undifferentiated PC12 cells over a range of manganese exposure concentrations (1, 10, 50, and 200 ,M MnCl2) and exposure durations (12, 24, 36, and 48 hr), to test the hypothesis that moderately elevated manganese exposure disrupts cellular iron regulation. Results demonstrate that manganese exposure produces a rapid and sustained dose-dependent dysregulation of cellular iron metabolism, with effects occurring as early as 12 hr exposure and at manganese doses as low as 1 ,M. Manganese exposure altered the dynamics of IRP-1 binding and the intracellular abundance of IRP-2, and altered the cellular abundance of transferrin receptor, ferritin, and mitochondrial aconitase protein levels. Cellular levels of labile iron were significantly increased with manganese exposure, although total cellular iron levels were not. The overall pattern of effects shows that manganese produced an inappropriate cellular response akin to iron deficiency, to which the cells were able to mount a compensatory response. Consistent with our previous studies, these data indicate that even low to moderate exposures to Manganese in vitro significantly disrupt cellular iron metabolism, which may be an important contributory mechanism of manganese neurotoxicity. © 2006 Wiley-Liss, Inc. [source] Whole Blood Manganese Concentrations in Dogs with Congenital Portosystemic ShuntsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 1 2010A.G. Gow Background: Manganese (Mn) is an essential mineral that is a cofactor for many enzymes required in the synthesis of proteins, carbohydrates, and lipids. Because hepatic clearance is essential in Mn homeostasis, conditions in humans resulting in hepatic insufficiency including cirrhosis and both acquired and congenital portosystemic shunting have been reported to result in increased blood Mn concentrations and increased Mn content in the central nervous system. Because Mn toxicity causes neurologic disturbances, increased Mn concentrations have been implicated in the pathogenesis of hepatic encephalopathy. Hypotheses: Dogs with congenital portosystemic shunts (cPSS) have significantly higher whole blood Mn concentrations than do healthy dogs or those with nonhepatic illnesses. Animals: Eighteen dogs with cPSS, 26 dogs with nonhepatic illnesses, and 14 healthy dogs. Methods: Whole blood Mn was measured by graphite furnace atomic absorption spectrometry. The diagnosis of cPSS was made by ultrasonography or during celiotomy either by visual inspection of a shunting vessel or portovenography. Results: Dogs with a cPSS had significantly higher whole blood Mn concentrations than did healthy dogs and dogs with nonhepatic illnesses. Whole blood Mn concentrations were not significantly different between healthy dogs and dogs with nonhepatic illnesses. Conclusion and Clinical Importance: Dogs with a cPSS have significantly increased whole blood Mn concentrations. Additional studies are warranted to investigate the role of Mn in cPSS-associated hepatic encephalopathy. [source] Role of circulating neurotoxins in the pathogenesis of hepatic encephalopathy: potential for improvement following their removal by liver assist devicesLIVER INTERNATIONAL, Issue 2003Roger F. Butterworth Abstract Both acute and chronic liver failure result in impaired cerebral function known as hepatic encephalopathy (HE). Evidence suggests that HE is the consequence of the accumulation in brain of neurotoxic and/or neuroactive substance including ammonia, manganese, aromatic amino acids, mercaptans, phenols, short-chain fatty acids, bilirubin and a variety of neuroactive medications prescribed as sedatives to patients with liver failure. Brain ammonia concentrations may attain levels in excess of 2 mm, concentrations which are known to adversely affect both excitatory and inhibitory neurotransmission as well as brain energy metabolism. Manganese exerts toxic effects on dopaminergic neurones. Prevention and treatment of HE continues to rely heavily on the reduction of circulating ammonia either by reduction of gut production using lactulose or antibiotics or by increasing its metabolism using l -ornithine- l -aspartate. No specific therapies have so far been designed to reduce circulating concentrations of other toxins. Liver assist devices offer a potential new approach to the reduction of circulating neurotoxins generated in liver failure. In this regard, the Molecular Absorbents Recirculating System (MARS) appears to offer distinct advantages over hepatocyte-based systems. [source] Increased metal allergy in patients with failed metal-on-metal hip arthroplasty and peri-implant T-lymphocytic inflammationALLERGY, Issue 8 2009P. Thomas Background:, In 16 patients with revised metal-on-metal arthroplasty and peri-implant lymphocytic inflammation, we verified the role of metal hypersensitivity by patch testing (PT) and lymphocyte transformation test (LTT). Methods:, In the 16 patients with lymphocyte dominated periprosthetic inflammation, allergy history was obtained by a questionnaire, specific serum IgE to aeroallergens was measured to assess atopy, PT to standard and metal series was performed and metal sensitivity was further assessed by LTT using blood mononuclear cells. Results:, Revision surgery was performed because of pain (8/16), osteolysis (4/16), dislocation (3/16) and loosening of the stem (1/16). Histological examination showed perivascular infiltrates of T lymphocytes, high endothelial venules, fibrin exudation and accumulation of macrophages with drop-like inclusions. Five patients had a history of cutaneous metal allergy and atopy was found in 25% of the patients. In 13/16 patients (81%), systemic metal sensitivity was found based on PT and/or LTT. Patch test reactions were seen in 11/16 patients (69%; partly multiple reactions/patient): 7/16 to Cobalt (Co), 7/16 to Chromium (Cr), 4/16 to Nickel (Ni), and one each to Molybdenum (Mo) and Manganese (Mn). Ten of 16 patients (62%) showed enhanced LTT reactivity to metals: 7/16 to Ni, 7/16 to Co, 5/16 to Cr, 5/16 to Mo and 4/16 to Mn. Conclusions:, The lymphocyte dominated peri-implant inflammation may well reflect an allergic hyper-reactivity in these patients, given the high rate of concomitantly found metal allergy. Despite the overall incidence of metal implant allergy being low, allergic reactions should be included as differential diagnosis in failed metal-on-metal arthroplasty. [source] Manganic encephalopathy due to "ephedrone" abuseMOVEMENT DISORDERS, Issue 9 2007Yanush Sanotsky MD Abstract We describe the clinical and neuroimaging features of 6 drug-abuse patients with self-inflicted manganese poisoning. The patients injected a home-brewed mixture called "ephedrone" (slang term) that contained manganese to produce an amphetamine-like euphoria. The desired chemical product, phenylpropanoneamine (also called methcathinone), was synthesized from a common-cold,remedy compound using permanganate as the catalyst. Manganese was a by-product in the ephedrone mixture. After months of self-injections, a clinical picture emerged, consisting of apathy, bradykinesia, gait disorder with postural instability, and spastic-hypokinetic dysarthria. There was no response to levodopa. The MRI revealed symmetric hyperintense T1-weighted signals in the basal ganglia, typical of manganese accumulation. © 2007 Movement Disorder Society [source] Managing the manganese: molecular mechanisms of manganese transport and homeostasisNEW PHYTOLOGIST, Issue 3 2005Jon K. Pittman Summary Manganese (Mn) is an essential metal nutrient for plants. Recently, some of the genes responsible for transition metal transport in plants have been identified; however, only relatively recently have Mn2+ transport pathways begun to be identified at the molecular level. These include transporters responsible for Mn accumulation into the cell and release from various organelles, and for active sequestration into endomembrane compartments, particularly the vacuole and the endoplasmic reticulum. Several transporter gene families have been implicated in Mn2+ transport, including cation/H+ antiporters, natural resistance-associated macrophage protein (Nramp) transporters, zinc-regulated transporter/iron-regulated transporter (ZRT/IRT1)-related protein (ZIP) transporters, the cation diffusion facilitator (CDF) transporter family, and P-type ATPases. The identification of mutants with altered Mn phenotypes can allow the identification of novel components in Mn homeostasis. In addition, the characterization of Mn hyperaccumulator plants can increase our understanding of how plants can adapt to excess Mn, and ultimately allow the identification of genes that confer this stress tolerance. The identification of genes responsible for Mn2+ transport has substantially improved our understanding of plant Mn homeostasis. [source] IR-SE and IR-MEMRI allow in vivo visualization of oscine neuroarchitecture including the main forebrain regions of the song control systemNMR IN BIOMEDICINE, Issue 1 2006Ilse Tindemans Abstract Songbirds share with humans the capacity to produce learned vocalizations (song). Recently, two major regions within the songbird's neural substrate for song learning and production; nucleus robustus arcopallii (RA) and area X (X) are visualized in vivo using Manganese Enhanced MRI (MEMRI). The aim of this study is to extend this to all main interconnected forebrain Song Control Nuclei. The ipsilateral feedback circuits allow Mn2+ to reach all main Song Control Nuclei after stereotaxic injection of very small doses of MnCl2 (10,nl of 10,mM) into HVC of one and MAN (nucleus magnocellularis nidopallii anterioris) of the other hemisphere. Application of a high resolution (80,µ) Spin Echo Inversion Recovery sequence instead of conventional T1-weighted Spin Echo images improves the image contrast dramatically such that some Song Control Nuclei, ventricles, several laminae, fibre tracts and other specific brain regions can be discerned. The combination of this contrast-rich IR-SE sequence with the transsynaptic transport property of Manganese (Inversion Recovery based MEMRI (IR-MEMRI)) enables the visualization of all main interconnected components of the Song Control System in telencephalon and thalamus. Copyright © 2006 John Wiley & Sons, Ltd. [source] Iron, Manganese and Copper Equilibria with Wood Fibres in Single Salt Aqueous SuspensionsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2005Robin Susilo Abstract Ions of Fe, Mn and Cu were introduced into suspensions of protonated or metal-free fibres and the equilibrium concentration of each metal in the fibre and surrounding solution was measured. The results were compared with the Donnan equilibrium model. Mn and Cu concentrations on the fibres were found to be pH dependent and in agreement with the model. An increased amount of Fe on the Kraft pulp fibres was found and attributed to iron containing precipitates trapped within the fibres. Precipitates in mechanical pulps had a very small amount (1-2 wt%) of iron. Des ions de Fe, Mn et Cu ont été introduits dans des suspensions de fibres protonatées ou « sans métaux » et la concentration d'équilibre de chaque métal dans la fibre et la solution environnante a été mesurée. Les résultats ont été comparés avec le modèle d'équilibre de Donnan. On a trouvé que les concentrations de Mn et Cu sur les fibres étaient dépendantes du pH et en accord avec le modèle. Une quantité accrue de Fe a été trouvée sur les fibres de pâte kraft et attribuée aux précipitats contenant du fer retenus dans les fibres. Les précipitats dans les pâtes mécaniques ont une très petite quantité (1-2% en poids) de fer. [source] Histidine-stimulated divalent metal uptake in human erythrocytes and in the erythroleukaemic cell line HEL.92.1.7THE JOURNAL OF PHYSIOLOGY, Issue 2 2004F. Oakley The uptake of 65Zn by human erythrocytes was investigated in the presence of high (40 mm) and low (5 mm) concentrations of histidine and 0,500 ,m cobalt, nickel, manganese and zinc. Varying concentrations of metal mono- and bis-histidine complexes will be formed and the inhibition of 65Zn uptake could be correlated with the calculated complex concentrations to investigate competition between metals. For each metal, the calculated concentrations of bis-histidine complex giving 50% inhibition of 65Zn uptake were similar at both 5 mm and 40 mm histidine. Manganese,bis-histidine appeared to have a much higher affinity for the binding site than the other metal,bis-histidine complexes, which had similar affinities to each other. Studies of the inhibition of histidine-stimulated 54Mn uptake by the addition of manganese confirmed that manganese,bis-histidine does act as a substrate for the transporter in a similar fashion to the other metals studied. In addition, human erythroleukaemic cells (HEL cells) were used as a model for erythroid precursor cells. l -histidine, but not d -histidine, stimulated 65Zn uptake in a saturable fashion. The other metals competed with zinc in a similar manner to that seen in erythrocytes, and the affinity for manganese,bis-histidine was much greater than for the bis-histidine complexes of the other three metals. Both the capacity for metal transport per cell, and the affinity of the transporter for the metal,bis-histidine complexes, were much greater in the HEL cells than in the erythrocyte. It is suggested that histidine-stimulated metal transport may play a role in the supply of metals to maturing erythroid cells. [source] Unprecedented Rate Enhancements of Hydrogen-Atom Transfer to a Manganese(V),Oxo Corrolazine Complex,ANGEWANDTE CHEMIE, Issue 30 2010Katharine Überragende Reaktivität: Ein Mangan(V)-Oxo-Porphyrinoid zeigt nach Zugabe eines anionischen axialen Liganden (X,=F, oder CN,; siehe Schema) eine stark beschleunigte Wasserstoffabstraktion. Dichtefuntionalrechnungen stimmen bestens mit dem Experiment überein und bieten Einblick in die Ursprünge dieser bemerkenswerten Ligandeneffekte. [source] Striking Inflammation from Both Sides: Manganese(II) Pentaazamacrocyclic SOD Mimics Act Also as Nitric Oxide Dismutases: A Single-Cell Study,ANGEWANDTE CHEMIE, Issue 25 2010Beseitigung von Zellgiften: Ein MnII -Pentaazamakrocyclus kann NO., O2., und Produkt ONOO, abfangen, wie Echtzeit-Amperometrie an einzelnen Zellen zeigt. Der Komplex (siehe Struktur) ist die erste Verbindung, die die zytotoxische Wirkung von reaktiven Sauerstoff- (ROS) und Stickstoffspezies (RNS), wie sie in Entzündungsreaktionen auftreten, komplett unterdrücken kann. [source] Manganese(II) and cobalt(II) complexes of 1,4-bis(diphenylphosphinoyl)butaneACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Anthony M. J. Lees The title complexes, catena -poly[[[diaquadiethanolmanganese(II)]-,-1,4-bis(diphenylphosphinoyl)butane-,2O:O,] dinitrate 1,4-bis(diphenylphosphinoyl)butane solvate], {[Mn(C2H6O)2(C28H28O2P2)(H2O)2](NO3)2·C28H28O2P2}n, (I), and catena -poly[[[diaquadiethanolcobalt(II)]-,-1,4-bis(diphenylphosphinoyl)butane-,2O:O,] dinitrate 1,4-bis(diphenylphosphinoyl)butane solvate], {[Co(C2H6O)2(C28H28O2P2)(H2O)2](NO3)2·C28H28O2P2}n, (II), are isostructural and centrosymmetric, with the MII ions at centres of inversion. The coordination geometry is octahedral, with each metal ion coordinated by two trans ethanol molecules, two trans water molecules and two bridging 1,4-bis(diphenylphosphinoyl)butane ligands which link the coordination centres to form one-dimensional polymeric chains. Parallel chains are linked by hydrogen bonds to uncoordinated 1,4-bis(diphenylphosphinoyl)butane molecules, which are bisected by a centre of inversion. Further hydrogen bonds, weak C,H...O interactions to nitrate anions, and weak C,H..., interactions serve to stabilize the structure. This study reports a development of the coordination chemistry of bis(diphenylphosphinoyl)alkanes, with the first reported structures of complexes of the first-row transition metals with 1,4-bis(diphenylphosphinoyl)butane. [source] | ||||||||||||||||||||||||||||||||||||||||||||||||||||